AU5676490A - Fluid condition monitoring and controlling system for a metalworking fluid central system - Google Patents

Description

FLUID CONDITION MONITORING AND CONTROLLING SYSTEM FOR A METALWORKING FLUID CENTRAL SYSTEM

Field of the Invention The present invention relates to central systems for recirculating metalworking fluid to a plurality of machine tools, and more particularly, to a method and apparatus for monitoring and controlling the condition of the cooling and lubricatiny fluid recirculated through such a central system. Background of the Invention

Machine tools conventionally employ metal¬ working or cutting fluid to lubricate and cool the cutting interface between the tool and the workpiece. These fluids serve the purpose of cooling and lubri¬ cating and in addition carry away the shavings and chips of material cut from the workpiece.

Metalworking facilities typically employ a number of cutting tools, many of which require similar metalworking fluids. Such facilities often employ what is referred to as the metalworking fluid central system. The central system collects and stores the metalworking fluid from a plurality of machine tools in a common reservoir and filters and recirculates the fluid between the reservoir and the tools.

In many metalworking applications, it is preferred to utilize water-based cutting fluids to take advantage of a higher heat absorption capacity than that provided by oils and non-soluble fluids. In addition, water-based fluids are preferred in many applications because they are less likely to contami- nate the air and other aspects of the working environ¬ ment within the facility. In addition, many water- based fluids are more economical, particularly when it is taken into account that they are biodegradable and rr.c_y be more easily disposed of than petroleum based or other oil or organic based fluids. In addition, water-based fluids are generally not as flammable or explosive and thus less hazardous.

Water-based fluids, however, introduce other problems. Water-based fluids are more susceptible to loss by evaporation, provide a medium for the growth of biological contaminants, and, because of their biodegradability, are prone to attack by the micro¬ organisms which can grow within them.

Water-based metalworking fluids generally fall into three categories. In one category includes soluble oils which are generally mineral oil. Another type of water-based metalworking fluid is the semi- synthetic fluid which is made up in part of mineral oil and in part by a combination of other synthetic lubricants. A third type of water-based metalworking fluid is the synthetic fluid which is made up entirely of synthetic components. The choice of cutting fluid is usually dictated by the particular machine opera¬ tion and materials being worked.

With water-based metalworking fluids, a number of components are added to the water-based fluid solution in addition to the soluble oil or synthetic lubricant which provides the basic lubri¬ cating function. The additives include corrosion inhibitors which will coat the workpiece, the removed chips and the other metallic parts of the tools and other machine components which are subject to oxida¬ tion. In addition, emulsifiers are added to retain and disperse the oils throughout the solution so that they are available to provide lubrication at the point of cut. Corrosion protection is usually provided by the introduction of organic salts into the solution. Microbiocides are also an important component of water-based metalworking fluid systems. The water- based medium, in addition to the organic lubricant which provides food for microorganisms, requires biocidal ingredients to inhibit the growth of bacteria and mold. Other specific components are also required for various specific applications to maintain the appropriate fluid properties to cool and lubricate the particular cutting operation. The addition of buffers are added as well as caustic or other substances to control or alter the pH of the fluid. Important in maintaining central systems is the desire that the properties of the cutting fluid be kept within controlled limits. The operating domain of the cutting fluids is generally a hostile environ¬ ment in which many factors are at work which alter and degrade the cutting fluid. In addition to an overall degradation of the fluid, many specific cutting fluid properties and components are disproportionately affected when the environmental factors are allowed to act on the fluid. In addition to degradation of the fluid, loss of fluid occurs through evaporation, through the splashing out of fluids from the system, and from the carrying off of fluids on the parts and on the chips which are carried away. This may change the fluid volume and may also change the concentration. of the various fluid components.

Evaporation, for example, will cause a loss of the water and also a loss of various fluid compo¬ nents in relation to their volatility. The carry-off phenomenon is more likely to deplete the lubricating oil component of a fluid which adheres to the parts and chips which are removed from the system. This is most often responsible for a loss in concentration of the corrosion inhibitors which, by their nature, adhere to the parts and the metal chips. Accordingly, make-up water must be added regularly. Oil or lubri¬ cant concentrates must be added to maintain their concentration in the fluid solution. Corrosion inhibitors must also be added to the fluid to compen¬ sate for their selective depletion.

The reservoirs of most central systems are usually located below floor level and thus are easily contaminated with bacteria and mold laden material.

Such microorganisms breed in the solutions, attacking the emulsifiers, corrosion inhibitors and lubricant materials of the metalworking fluid. In addition, other lubricating and hydraulic oils and other foreign materials enter the metalworking fluid, some becoming emulsified within the fluid. These generally are a detriment to the fluid's performance and to the dura¬ tion of its life.

Maintenance of a metalworking fluid central systems requires a controlling of the various prop¬ erties and components of the metalworking fluid. Loss of cooling and lubricating capacity of the fluid can produce expensive and damaging results by increasing the production of scrap and by decreasing the life of tools and other machine components. A failure to control the properties of the fluid which prevent corrosion of the parts and cuttings results in increased waste due to the corrosion. In addition, increased contamination of the system with oxidation products reduces the lubricating effects of the fluid and the fluid's useful life. Furthermore, a serious problem with water- based fluids results from failure to control microbio¬ logical growth in the metalworking fluid. Micro¬ organisms in the fluid will, up to a point, grow with increasing rapidity if their growth is not checked in an early stage. The growth of these organisms tends to alter the system pH and otherwise change the environment in such a way as to facilitate increased growth rate of the micro-organisms. Since microorga¬ nisms feed on the lubricating components and other organic components of the fluid, they degenerate or degrade the fluid to the point where it loses its ability to lubricate, protect the parts, or to other¬ wise perform its function. This can prematurely end the life of the oil, accelerating the need for a complete replenishment of the fluid in the system. Fluid replacement may involve significant downtime, substantial cost for the replacement fluid, and additional expenditures in disposal of the spent fluids in accordance with environmental criteria. The methods employed in the prior art to determine the conditions of the fluid, in order to respond to changes in the fluid conditions have been inadequate to properly maintain the fluid. The common method of monitoring the properties of metalworking fluids has been to extract a sample of the fluid from the system, remove it to a laboratory, and perform a wet chemistry analysis upon the sample. Such proce¬ dures are generally regarded as capable of performing an accurate analysis on the properties of the fluid at the time, and under the conditions upon which, the test is made. However, the procedures are slow and, in many cases, changes in the sample result between the time the sample is taken and the time at which it is analyzed. This method of testing often produces data which are out of date due to the testing delay or inaccurate due to the change in the property being measured subsequent to the drawing of the sample.

Accordingly, corrective action taken is often too slow or at the wrong level to correct for the actual condition of the fluid at the time the correcting action is carried out. Thus, the cor- rections have been insufficient, resulting in consid¬ erable instability in the fluid property maintenance. As a consequence poor fluid performance results. Furthermore, the prior art systems have not resulted in the collection of data regarding the fluid's properties in a combination sufficient to make it possible to detect and determine the causes of fluid problems and to indicate the appropriate corrective response. Summary of the Invention

It has been a primary objective of the present invention to provide a method and apparatus for monitoring and controlling a metalworking fluid in a metalworking fluid central system servicing a plurality of machine tools. It has been a further objective of the present invention to provide a quick and accurate system for measurement of metalworking fluid parameters in real time so as to facilitate accurate and responsive correction of deviations from ideal fluid conditions so that the fluid performance may be effectively and satisfactorily maintained. It is a more particular objective of the present invention to provide a method and apparatus by which metalworking fluid monitoring data can be quickly and accurately collected from a plurality of metalworking fluid central systems and analyzed at a remote location from which determinations can be made for corrective control of the fluid to be performed on a real time basis. It is an additional objective of the present invention to provide such a method and apparatus in which the monitored data may be processed and decision making commands initiated to automatical¬ ly control the chemical composition and physical characteristics of a metalworking fluid to maintain the fluid within certain controlled parameters.

According to principles of the present invention, a metalworking fluid central system is provided with inline monitors for measuring fluid properties by the provision of a plurality of inline sensors responsive to a plurality of different fluid properties. The sensors generate real time output signals responsive to levels, changes or trends in the sensed parameter values. The parameters sensed include among those sensed parameters relating to specific chemical components of the fluid, preferably, dissolved oxygen gas concentration and hydrogen ion concentration (pH) . In accordance with the preferred embodiment of the invention, other parameters sensed include electrical conductivity and temperature. This data is digitized and stored in a storage medium through a computer located at the central system. In accordance with a further preferred embodiment of the present invention, the central system is also provided with a plurality of additive sources connected through pumps, valves or other fluid control devices to inject make-up water, lubricant concentrate, buffers, micro- biocides and other such additives in order to provide for various actions which would be indicated by the measurements to correct the properties of the fluid. Such devices are linked through a controller having inputs driven directly by the computer, and by con¬ trols manually operated in response to messages displayed as a result of the processing of the measured data by the computer. Further in accordance with a preferred embodiment of the present invention, the computer is linked through a conventional modem to a telephone switching network. This central system and other central systems which are also provided with oni- toring and controlling features of the invention and similarly linked through the telephone switching network, are selectively connectable to computerized equipment at a remote central office supervising facility. The computer at the central station or center is programmed so as to periodically establish a communications link through the telephone exchange with each of the various machining facilities to extract data collected and stored in the central system computer for transfer to and analysis at the central location. Preferably, the interrogation to collect data for analysis occurs at programmed inter¬ vals of, for example, 24 hours, with more frequent checks made for unusual or alarm conditions. This data may be used^• in whole or in part either through the computer at the central system or from the centra processing center to establish automated commands to signal or directly control the introduction of variou additives to correct- parameters of the fluid. Pref¬ erably, the data is analyzed and decisions made at least in part with operator or manual intervention at the central or machine location to either take correc- tive action or override automated corrective commands. The information may preferably include data from a plurality measurements taken at spaced timed inter¬ vals, preferably hourly, which may be analyzed at the central monitoring center and trends of the fluid in the respective central systems determined for estab¬ lishing and supervising a maintenance program, to schedule maintenance visits and to dispatch supplies of chemical components to the various facilities.

The advantages of the present invention are that data can be gathered which is accurately derived from inline samples, is representative of the real time condition of the fluid and is available for real time decision making and response in time make the corrections necessary to effectively maintain control of the fluid. As a result, the life of the fluid is lengthened, the ability to quickly and rapidly respond to fluid changes is provided, and significant and accelerating degeneration of the fluid is prevented, along with the resulting loss in fluid performance, increase in waste, and increase in cost of the opera¬ tion. These and other objectives and advantages of the present invention will be more readily apparent from the following detailed description of the drawings in which: Brief Description of the Drawings

Fig. 1 is a block diagram of a metalworking fluid central system which includes the fluid moni¬ toring and control system in accordance with princi¬ ples of the present invention; Fig. 2 is a schematic diagram of the central system sensor module of the system of Fig. 1;

Fig. 2A is a diagrammatic cross-sectional view taken on lines 2A-2A showing the fluid flow patt rn within the sampling chamber of the monitor of Fig. 2;

Figs. 3-10 are graphs generated by the system of Fig. 1 illustrating data analyzed in accor¬ dance with the present invention;

Figs. 3-6 are graphs of the operation of one metalworking fluid central system operating under controlled conditions and respectively plotting temperature, conductivity, pH and dissolved oxygen as a function of time;

Figs. 7 and 8 are graphs similar to Figs. 3-6 of the operation of another metalworking fluid central system which is biologically out of control and respectively plotting conductivity and dissolved oxygen as a function of time; and

Figs. 9 and 10 are graphs similar to Figs. 3-8 of the operation of another metalworking fluid central system experiencing a fluid containment failure and respectively plotting dissolved oxygen and pH as a function of time.

Referring to Fig. 1, a metalworking fluid monitoring and control system 10 according to the principles of the present invention is illustrated. In the preferred and illustrated embodiment there represented, the monitoring and control system 10 is a multifacility monitoring and control system dis¬ tributed among a plurality of diverse locations which include a central information monitoring data analysis and supervisory location 11, a plurality of different¬ ly located metalworking plants 12, 12a, and 12b, and a communication system 13 through which are established communications links between the central location 11 and each of the plants 12, 12a, 12b. Preferably, the communications link 13 is a public telephone commu¬ nications system which includes one or more telephone switching networks 14 of the various public or private telephone systems for routing telecommunications information between the telephone line 15 between the central location 11 and the telephone exchange 14 and the telephone lines 16, 16a and 16b which connect the telephone exchange 14 with the respective plants 12, 12a, 12b. It should be readily appreciated that, while telephone lines 15, 16, 16a and 16b are described as wires, other transmission media may make up the communications links, and that alternatives to the preferred telephone communications approach may be employed.

At the central location 11 is a metalworking fluid monitoring center 20 which includes a computer 21 connected through a modem 22 to the telephone line 15. The computer 21 has connected thereto a data storage medium 23, which is preferably a disk or other non-volatile data storage medium, a printer 24 which is capable of generating hard copies of visually perceivable data, data records or files, a monitor 25 which is capable of online and random access display of the information which passes through or is stored in the computer 21, and a keyboard or other computer/- supervisor interface device 26. The system 10 components present at each of the plants 12, 12a, 12b are diagrammatically illus¬ trated for plant 12 in Fig. 1. The plant 12 is a metalworking facility which is equipped with a metal¬ working fluid central system 30. The system 30 operates to recirculate a cutting or metalworking fluid through a fluid reservoir 31 to and through a plurality of machine tools 32. The reservoir 31 is divided into two parts, a clean fluid tank 33 and a dirty fluid tank 34. The clean fluid tank 33 contains a level of metalworking fluid 35 in its clean and controlled condition as supplied to the machine tools 32. The dirty fluid tank 34 receives the used fluid 36 which is returned from the machine tools 32 after use. The dirty fluid 36 is the portion of the clean fluid 35 which also includes solid metal chips and other particulates 37 which precipitate to the bottom of the tank 34 and fine suspended particulates 38 which are separated from the fluid 35 in a filter 39.

The central system 30 includes a fluid recirculating network 40 for recirculating the fluid 35 through the reservoir 31, through the machine tools 32 and back to the reservoir 31. The reservoir 31 is typically positioned within the pit 41 below the floor level 42 of the plant 12. The machine tools 32 are generally mounted on the floor 42 to stand thereabove. The recirculating system 40 includes a fluid pump 44 located within the pit 41 adjacent the reservoir 31 and having inlet 45 connected with the clean fluid tank 33 in such a way as to draw clean fluid 35 from the tank 33. The pump 44 has its outlet connected to a supply line 46 which communicates through the floor 42 of the plant 12 to the inputs 47 of the machine tools 32 for deliverying clean cutting fluid 35 to the machine tools 32. At the machine tools 32, the fluid 35 is, in a manner conventional to and specific to these individual machine tools 32, provides a cooling and lubricating function at the point of cut between the cutting tool component and the workpiece. The fluid also carries from the cutting site dirty fluid

36 which is made up of the clean fluid 35, and chips

37 and other cut and foreign material from the work- pieces to remove it from the cutting site. The fluid 36 returns through metalworking fluid drain lines 48 from the machine tools 32 and then a return flume 50 within the floor 42 of the plant 12 to the dirty fluid tank 34.

A return flume 50 is often an open drain built within the floor 42 of the plant 12. Into the flume 50 drains not only the dirty fluid 36 from the lines 48, but also other foreign liquid and solid materials including solvents, spilt lubricants, and other contaminants. These contaminants flow with the fluid by gravity through the flume 50 which slopes downwardly into the pit 41 to a discharge opening 51 which empties the dirty fluids 36 into the return tank 34. In the tank 34, the chips and other cuttings 37 generally descend to the bottom. From the bottom of the tank 34, the chips 37 are removed from the return tank 34 by a drag out conveyor mechanism 53 which removes the chips 37 from the tank 34, transports them upwardly from the pit 41 to above the floor 42, and deposits them into a hopper 54 for recycling.

From the tank 34, the dirty fluid 36, less the removed chips 37, is pumped through a pump 56 into the filter 39 which removes other smaller dust and other solid particulates which have not precipitated to the bottom of tank 34 from the fluid to deliver cleaned fluid 35 to the clean fluid tank 33. Line 57 is the inlet line from the tank 34 for the pump 56. A fluid makeup system 60 is also provided to restore or add components to the fluid 35 within the reservoir 31. The makeup system 60 includes a supply line 61 which connects a plurality of component sources 62 with the tank 33. The sources 62 generally include a make up water supply line 63 which is connected from a pressurized source of clean supply water through a control valve 64 to the line 61. In addition, the makeup sources 62 of the makeup system 60 include a supply tank 65 of clean metalworking fluid concentrate through which the concentrate 66 is pumped through a pump 67 to the makeup fluid supply line 61 and into the clean fluid tank 33. In addition, a plurality of additive sources 68 are provided to supply different additives to the fluid 35. These additives are communicated through delivery systems which may include pumps or valves 69. The monitoring and control system 10 in¬ cludes a cutting fluid monitoring and control network 70 at the located plant location 12. The control network 70 includes a controller 72 for operating the equipment which delivers the additives from the make up system 60 to the fluid 35 in the reservoir 31. The controller 72 has a plurality of outputs 73 each of which connect to a different one of the control devices 64, 67 and 69 which regulate the addition of make-up water from the source 63, make-up concentrate from the source 65, and other fluid additives from the sources 68.

The network 70 also includes a computer 75, preferably an industrial grade programmable computer, having outputs 76, one of which connects through an output to the controller 72 for communicating command signals from the computer 75 to the controller 72. The computer 75 also has outputs 76 which connect to a monitor 77 and to a printer 78 for displaying, in visually perceivable form, information from the computer 75 for use by an operator 79 in entering control commands into the controller 72.

The monitor and control network 70 also includes a sensor module 80 which generates electrical output signals on a control line 81 connected to an input of the computer 75. The sensor module 80 contains a plurality of sensing devices for measuring characteristics of fluid 35 flowing therethrough. The module 80 is connected in-line with the fluid recir¬ culating system 40 so as to measure characteristics of clean recirculating fluid 35. The module 80 has an inlet 83 connectable to the supply line 46 and an outlet 84 connectable to the return flume 50. As such, a fluid bypass is formed from the supply line 46 past the machine tools 32 and to the return tank 34 of the reservoir 31. The sensor module 80 includes a temperature sensor 85, a pH sensor 86, a dissolved oxygen sensor 87 and a conductivity sensor 88. The sensors 85, 86, 87 and 88 measure respectively the temperature, pH, dissolved oxygen content and conductivity of the fluid 35 as it flows in line through the sensor module 80 and does so in real time. The outputs of the sensors 85-88 are communicated through the output line 81 to the computer 75. From the computer 75, the data from the sensor module 80 is stored in a data storage medium 91 at the network 70. In addition, the com¬ puter 75 connects through a modem 92 to the telephone line 16 so that the computer 75 will communicate through the telephone exchange 14 of the communica¬ tions network 13 with the computer 21 at the central location 11.

Referring to Fig. 2, the sensor module 80 is described in greater detail. The module 80 is a type of water monitor module manufactured by Schneider Instrument Company, 8115 Camargo, Road, Madeira, Ohio. The module 80 is shown having its inlet 83 connected to receive clean, or more precisely, clarified metal- working fluid 35 from the supply line 46 and to discharge the fluid 35 through the outlet line 84 to the return flume 50. The fluid 35 flowing through the module 80 is maintained at the proper pressure and flow rate by an inlet valve 101 connected in the line 83. From the valve 101 is a bank of feed pipes 103 which communicate the clarified fluid 35 to a sampling block 105 which contains the sensors 85, 86, 87 and 88. In the embodiment shown, the block 105 includes three bores 107, 109 and 111 each having at the bottom thereof an inlet 113, 115 and 117 respectively con¬ nected from the pipe manifold 103. The bores 107, 109 and 111 form sampling chambers 108, 110 and 112 therein. The inlets 113, 115 and 117 are positioned with respect to the chambers 108, 110 and 112 such that fluid entering the chambers does so with a swirling action to fill the chambers and to mix with the fluid therein to prevent separation of its compo¬ nents. At the tops of the chambers 108, 110 and 112 are respectively located outlet ports 119, 121 and 123 each connected to the outlet line 84. By this port arrangement, the fluid enters and swirls through the chambers to the outlets as shown with respect to chamber 108 in Fig. 2A. As such, the fluid in the chambers remains fresh and oil and other material which might have a tendency to float to the top of the fluid and collect in spots within the chambers 108, 110 and 112 will not have the opportunity to do so.

The cutting fluid 35 is continuously recir¬ culated through the chambers 108, 110 and 112 of the block 105 during sampling intervals. At various times between the sampling intervals, clean fresh water is circulated through the chambers 108, 110 and 112 in order to maintain the internal surfaces including sensors therein clean and extend their lives. This is provided by a water inlet and valve combination 124 connected as a by-pass line from the outlet line 84 to the inlet line 83 to operate alternately with the valve 101.

The pH sensor 86 is supported through a sealing cap 125 at the top of the chamber 108 to support the pH sensor 86 in spaced relationship from the walls of the chamber 108 and in the in-line stream of fluid 35 flowing through the chamber 108. Also in the chamber 108 is the temperature sensor 85. A sensor 85 may be provided in each chamber. In similar manner as with the sensor 86, the dissolved oxygen sensor 87 is supported through a cap 126 in the chamber 110 and the conductivity sensor 88 is sup¬ ported through a cap 127 within the chamber 112. The sensors 85, 86, 87 and 88 connect through output cable 81 to the inputs of a processing or computer module 130 which includes the computer 75 and the storage medium 91. The output from the sensors 86, 87 and 88 each go to a respective analyzer board 131, 132 and 133 respectively of a bank of analyzer boards 135 which may include inputs from other sensors. The output of the temperature sensor 85 is connected to the processor so as to interact with each of the boards 135. The reason for the connection of the temperature sensor to each of the boards is that the other three sensors measure prop¬ erties of the fluid 35 to determine characteristics of the fluiα 35 while the temperature sensor primarily collects information for temperature compensation of the other measurements. Accordingly, the information from the temperature sensor is required by the analy¬ sis performed by each of the boards 131, 132 or 133. The analyzer boards 135 operate to separate the measured signal from noise, to adjust the analog signals from the sensors and to convert the signals to corresponding digital signals.

Also within the module 130 is a power supply 141 which operates the components within the module 130 and delivers energy for the operation of the sensors 85, 86, 87 and 88. The module 130 also contains a memory board 143 which is connectable to each of the processing boards 135. The memory board 143 which contains a non-volatile EARAM for storing the processing program and which contains the data storage medium 91. The computer module 75 also includes a general processing board or CPU 145 which executes the program stored in the board 143. Together the boards 143 and 145 function to sample the probes 85, 86, 87, 88 at periodic intervals and to produce digital data corresponding to the regular sampling intervals regarding the measured characteris¬ tics of the fluid 35. Additionally, a communications board is provided which is generally an RS232C serial output board and modem 72. The communications board or modem 72 is connected to the telephone line 16 (as shown in Fig. 1) .

The controller board or computer 75 has the panel 151 having a first display 153 which operates in conjunction with a selector switch 155 so that the readings from each of the probes 85, 86, 87 and 88 may be independently displayed on the panel 153. The panel 153 is generally located above the controller 72 of Fig. 1. The panel 151 also contains a 24 hour real time clock 157. The components of the panel 151 are connected to the computer module CPU board 145. Referring again to Fig. 1, the operation of the monitoring and controlling system 10 is better understood. The monitor control network 70 at the plant 12 will- operate under control of the computer 75 to perform regular sampling measurements of tempera¬ ture, pH, dissolved oxygen content and conductivity of the fluid 35 inline and in real time as it circulates through the recirculating system 40 of the central system 30. These measurements are processed through the equipment which was been described in connection with Fig. 2 above and stored, preferably at hourly intervals in the data storage medium 91. This data may be tested in real time in accordance with algo¬ rithms stored in the program module of the computer 75 to test for alarm conditions. Upon the occurrence of an alarm condition, a signal is generated to alert the operator 79 through the monitor 77, printer 78, or control panel 151 (Fig. 2) to take corrective action. In addition, the alarm conditions, should they be detected, .according to certain embodiments of the invention, cause .the computer 75 to activate the modem 92 to connect the system 70 on line with the telephone line 16 to communicate the data through the telephone exchange 14 of the communications network 13 to the monitoring center 20 at the central location 11. In the normal course of operation, the monitoring center 20 at location 11 will periodically establish a telephone communication or other commu¬ nication link through the network 13 to the plant 12 so that the computer 21 will communicate via the modem 22 and modem 92 with the computer 75. This communica¬ tion will cause a transfer of the data stored in data storage medium 91 from the plant 12 to the central location 11. This communication established from the central location 11 will occur, typically, once per 24 hour period and will involve a transmission of records of data from the data storage medium 91, each time marked, to the computer 21 at the location 11. At the location 11, this information is processed in accor- dance with standard statistical process control techniques with software at the computer 21 and thereupon analyzed.

The interrogation by the monitoring center 20 o£ the plant 12, may occur typically once per day, but should take place at least at such intervals as will effectively result in analysis of the data in real time so that real time responses may be made to changes or trends which are revealed by the analysis of the data. By "real time" it is meant that an analysis is performed in sufficiently short proximity in time to when the test or data sampling has been made by the sensors of the sampling module 80 so that corrective action will be possible while the data is still valid and while the condition measured still exists both in a qualitative and quantitative sense. Such interrogation may be continuous or instantaneous if required or may be spaced at such intervals which are sufficiently short to provide real time analysis and real time response within the meaning of the terms as defined above.

The measured values of data will all be transmitted to the central monitoring center 20 at the central location 11. Of these values, it has been determined, in the preferred and illustrated embodi¬ ment, that temperature, conductivity, pH and dissolved oxygen should be measured simultaneously to provide related data groups for purposes of the analysis. It will be appreciated that measurement of other parame¬ ters may also be desirable, such as measurement of the concentrations of specific components of the fluid 35. The temperature measurement is important in that the temperature of the metalworking fluids 35 in a central system 30 may vary considerably during use. The changes in temperature of the fluid 35 occur with the changes in atmospheric temperature and with variations of the fluid temperature due to the use of the equipment. The temperature itself provides information regarding the events at the plant site 12 which may have a bearing on the condition of the fluid 35 and may be helpful in the interpretation of other data or in diagnosing causes of changes in fluid condition. In addition, and perhaps more importantly, the temperature of the fluid is important for per¬ forming temperature compensation upon other data and for interpreting the other measurements made of the fluid. Certain of these measurements are automatical¬ ly temperature compensated at the sensing module 80 and within the computer module 75 at the plant loca- tion 12. In addition, the measurement of temperature of the fluid 35 may itself be important particularly to high tolerance machine operations where dimensional changes caused by temperature may effect the quality of the parts produced. The temperature signal is derived in the first instance from the sensor 85.

The conductivity measurement is obtained from the conductivity sensor 88. The conductivity bears with the composition of the fluid 35. Measured conductivity will change as the concentration of the metalworking fluid in the water changes. In addition, dissolved solids in the fluids will also cause changes in the conductivity. Conductivity will provide a relative indication of concentrations of particular components. The identity of the particular components which are affecting conductivity changes depends on the amount of knowledge of a person or program inter¬ preting the data as with respect to the component in the solution which is most rapidly changing. Accord¬ ingly, the present invention provides for the simulta- neous real-time measurement of plural parameters of the fluid to facilitate identity of the causes of such data trends. Conductivity as a means for measuring concentration of a particular component of the fluid thus is most advantageously performed when interpreted in conjunction with such other data. It has been found that measuring of conductivity in conjunction with measurements of pH and dissolved oxygen, for example, provide considerable information as to the composition and composition changes in the fluid. With the conductivity measurement, relative changes in the measurement including particularly trends estab- lished by the changes and the rates of changes over time provide significant information of the nature of events occurring at the central system 30 which is being monitored.

The pH of the fluid 35 measured by the sensor 86 is a widely used electrochemical parameter employed in the management of metalworking fluid systems. It is found, however, that obtaining an accurate pH measurement is sometimes difficult. Measurement of pH is important in that maintaining a desirable pH at a level of, for example, 9.1, will reduce the growth of bacteria and other microorganisms within the fluid. pH may change from a number of sources such as with the introduction of substances into the fluid during the normal course of maintaining the central system 30. For example, the flushing of the return flume with solvents often affects the pH. Chemical action within the fluid may do the same. The introduction of contaminants during the normal course of operating the system may also effect the pH. It is necessary to add substances to the fluid from time- to-time in order to maintain the pH at a desirable level in order that the growth of microorganisms does not escalate.

The growth of microorganisms in a system, even a system with maintained pH, will nonetheless occur. When the system pH drops to, for example, a level of 8.5 or 8.6, the conditions for the growth of microorganisms, particularly bacteria, greatly in¬ crease. The growth of bacteria causes the expulsion of a substance which further tends to neutralize or lower the pH of the fluid. This may then cause the fluid to become even a more favorable environment for the growth of bacteria. This can in turn cause a rapid increase and escalation in the growth of bacte¬ ria such that, if not responded to quickly enough, can cause a total destruction or bacterial consumption and breakdown of the fluid.

The growth of micro-organisms such as bacte¬ ria will, in the first instance, cause a consumption of the oxygen dissolved in the fluid. Because of the high degree of agitation in the fluid and its exposure to ambient air, the dissolved oxygen in the fluid is usually near saturation, often even above the satur¬ ation point. Thus, the growth of bacteria can easily occur and substantial amounts of oxygen present in the fluid will support the bacterial growth. As bacteria grow, the oxygen level of the fluid will decline. A decrease in the dissolved oxygen content of the cutting fluid is often a very good indication of the ongoing growth of bacteria or molds.

Measurement of dissolved oxygen in order to establish ongoing trends by grab sampling of the fluid, as is done in the prior art, has proved an inaccurate method for deriving information in order to reliably detect microorganism growth. The inline measurement methods of the present invention, however, provide precise evenly spaced measurements of fluid oxygen content which may be developed at the moni- toring center 20 into accurate trend data. This trend data will reveal microorganism activity. Accordingly, comparison of this data with pH data taken simulta¬ neously with the dissolved oxygen measurements will allow for the determining of the causes of change in pH and for predicting possible destructive changes in the fluid composition which would result unless certain corrections are made. Furthermore, corre¬ lation of this data with the conductivity data regarding the composition of the fluid provides different sources of data which react differently to organic, biological, and ionic fluid components. These when analyzed from simultaneous measurements in accordance with the trends of each, provides for the detecting of fluid conditions which have not been previously realizable until employed in accordance with the present invention in combination. The system of Fig. l operates to perform the same monitoring functions on a plurality of different plant locations 12, 12a, 12b, etc., so that analysis and corrective action may be taken for a number of facilities and also so that the supervising of a maintenance program from the monitoring center 20 may be optimized in such a way as to efficiently supervise a number of central systems 30 at different plants 12. Figs. 3-10 show comparative data analyzed in accordance with the present invention for three different plants during separate time periods each spanning approximately 6 days. The first data sampling group is illustrated in connection with Figs. 3-6. Figs. 3-6 show typical data from a 27,000 gallon centerless grinder operation using semi-synthetic fluid in a high production precision parts manufac¬ turing process. On the graphs 3-10, the large marks are representative of days, each signifying midnight of the given day. The small marks represent hourly intervals at which the readings are taken as to provide a relatively continuous curve approximated by the curve in the figures. As Fig. 3 illustrates, a temperature profile over the period of approximately 6 days is illus¬ trated. The graph illustrates a significant tempera¬ ture variation over the period along with periodic small reductions in temperature. The slow wide fluctuations in temperature were, in this case, due to ambient temperature changes with the low point occur¬ ring when production slowed during a weekend period. The small period temperature reductions were caused, in this case, by regular batch additions of makeup fluid injected, for example, from a supply 63 of makeup water together with the addition of concentrate 66 from the concentrate source reservoir 65. These makeup sources were maintained at lower temperature than the fluid 35 recirculating in the central system 30 at the time they were added.

In Fig. 4, the conductivity of the same fluid plotted in Fig. 3 over the same time period is illustrated. The conductivity measurement is charac- terized by a plot of sawtooth profile as shown in Fig. 4. The portions of the curve which steadily increase demonstrate fluid concentration increases seen as a conductivity rise of the fluid due to evaporation of water from the system. Thus, the concentration of all components of the fluid are increasing during these periods at which the slope of the line shows conduc¬ tivity increase. The sudden step drops in conductivity correspond to the addition of make up fluid as was described in connection with Fig. 3. The combined data in Figs. 3 and 4 confirm that the addition of makeup fluid is responsible for the short term variations in the measured temperature and conductivity of the fluid. Additionally, the vertical displacement of the declining steps in Fig. 4 are an indication of the quantity of makeup fluid being added. Referring to Figs. 5 and 6, the measurements of pH and dissolved oxygen for the same fluid plotted in Figs. 3 and 4 are shown during the same interval of time. The relative smoothness of the graphs, particu¬ larly of the. dissolved oxygen plot of Fig. 6, shows that the system is relatively free of biological activity. The more rapid fluctuation of the pH curve of Fig. 5 shows however that concentrations of non- biological components are changing. For the first half of the graph, these fluctuations are within tolerable limits. The more severe spikes toward the second portion of the graph are indicative of the addition of specific additives to the system during that portion of the time period. Generally, the condition of the fluid depicted in Figs. 3-6 shows a relatively well behaved fluid and one which is within control limits. The combination of graphs of Figs. 7 and 8 and the combination of Figs. 9 and 10 show abnormal conditions of fluid in two different systems. The conditions shown in Figs. 7 and 8 are examples of a mechanical failure of a central system 30 which shows up on the data monitored at the monitoring center 20.

Referring to Figs. 7 and 8, the conductivity and dissolved oxygen respectively are illustrated in connection with a 2700 gallon central system and aluminum can drawing facility. The abnormal condition which occurred was the undetected rupturing of a pipe in a water cooling line which occurred about midway through the time period depicted by the charts of Figs. 7 and 8. The jagged characteristic on the conductivity chart of Fig. 7 reflects the automatic fluid makeup which causes the introduction of clean fluid from the water supply line 63 and the concen¬ trate tank 65 into the central system 30. This fluid addition generally causes a decline in conductivity as the other components of the fluid which tend to increase the conductivity are diluted.

The data shown on the charts of Figs. 7 and 8 follow a period during which the system experienced considerable difficulty in maintaining a proper mix ratio and pH stability. An unidentified leak was apparently the cause which was manifested by the measurements taken during the period shown in the graphs of Figs. 7 and 8 when the leakage problem becomes worse. This more serious leakage problem is coincident with the significant drop in conductivity shown in Fig. 7 from approximately 3,000 micromhos to approximately 2,600 micromhos during a period of approximately 24 hours. The drop in conductivity was caused by the replacement of the leakage fluid with makeup fluid of lower conductivity which maintained the fluid level in the reservoir 31 approximately constant. In the system depicted here, the leak was repaired and the conductivity then rose as shown in Fig. 7 as the fluid component concentrations were reestablished by the addition of additives.

As Fig. 8 illustrates, however, the unde- tected leak prior to the measured period resulted in bacteria growth which was due to loss of bacteriacides in the fluid. This was brought back to a normal level by the addition of additives which then cause the dissolved oxygen to be maintained for a period as shown in Fig. 8. Specifically, with the increase leakage which corresponds to the declining conduc¬ tivity of Fig. 7, the fluid again became very lean and the growth of microorganisms gradually increased following the dilution of the fluid. This microbio- logical growth caused a decrease in the dissolved oxygen which was reflected by the decrease shown in Fig. 8. After the leakage problem was corrected, the addition of bacteriacides restored the dissolved oxygen and checked the bacterial growth.

Referring to Figs. 9 and 10, the dissolved oxygen and pH of a central system 30 of approximately 17,000 gallons utilizing a semi-synthetic metalworking fluid for machining operations upon aluminum housings is illustrated. The central system 30 in question had severe mold growth. In the plots illustrated in Figs. 9 and 10, the facility had a routine practice of adding microbiocide at double strength on Fridays and on Sunday mornings before shutting down for the weekend and restarting the system for the next week. The severe mold growth of the system did not show up on culture counts performed by the facility but the mold could be visually seen in the tank 31 and return flume 46 and removed mechanically.

Referring to Fig. 9, the extremely low dissolved oxygen content plotted is characteristic of the condition inducive to mold growth. The vertical rises in dissolved oxygen coincide with the addition of biocide. The effect of these additions, however, as shown in Fig. 9 was significant but temporary. In the pH chart of Fig. 10 it is seen that the pH began to increase with the addition of microbiocide but that this impact too was shortlived. The condition illus¬ trated in Figs. 9 and 10 was such that a replacement of the fluid and a cleaning of the system was required in that the mold growth of the system had gone beyond the point of controllability by chemical means.

According to the embodiment of the invention illustrated, data of the type described above can be manually analyzed or, through the provision of appro¬ priate algorithms, automatically analyzed. The algorithms may be simple stored tables which contain data or curves of information acquired from previous measurements or experience with the specific system being controlled, or similar systems, correlating parameter variations with corrective actions which have proved effective. Preferably, a combination of both automated and manual analysis and decision making is employed to control the central systems 30 of the plants monitored in accordance with the system depicted in Fig. l to control the fluids in accordance with commands instituted in response to the analyzed data. In response to such analysis, control signals are initiated either through the remote communication system 13 from the central location 11 to the plants 12, 12a, 12b or by other methods intended to communi¬ cate the action needed to correct the system devia¬ tions detected by the monitoring process. This control information may be input to the controller 72 either through the computer 75 in response to informa¬ tion received through the modem 92 or through a panel on the controller 72 by the manual acts of the operator 79 then in response to data provided to him on the monitor 77 or printer 78. The information is provided either in the form of data from the computer 75 or in the form of commands or recommendations from the central monitoring center 20 at the location 11.

Having described the invention, what is claimed is the following:

Claims (30)

1. A method of determining the condition of an aqueous cutting fluid in a recirculating fluid central system serving a plurality of metalworking machines, the method comprising the steps of: maintaining a central reservoir containing a volume of aqueous metalworking fluid sufficient to service the machines; recirculating the fluid through the reser¬ voir and the machines; monitoring in-line the recirculating fluid; and generating a signal in real-time carrying information regarding a component parameter of the monitored fluid.

2. The method of claim 1 further comprising the step of: controlling in real time the condition of the fluid in response to the generated signal.

3. The method of claim 2 wherein the control¬ ling step comprises the step of: adding a fluid component to the monitored fluid in response to the generated signal.

4. The method of claim 3 wherein the adding step comprises the step of: controlling a flow control device connected with the central system and the supply of the fluid component to add the component to the monitored fluid.

5. The method of claim 1 further comprising the step of: comparing the generated signal with stored parameter values corresponding to a desired condition of the fluid, and changing the composition of the monitored fluid in accordance with the results of the comparison to maintain the condition of the monitored fluid within a predetermined limit of the desired condition.

6. The method of claim 3 wherein the informa¬ tion carried by the generated signal relates to the difference between the component parameter of the fluid as monitored and a desired value of the compo¬ nent parameter, and wherein the added component is a component which, when added, will tend to reduce the difference.

7. The method of claim 1 wherein said signal includes a plurality of information signals each carrying information regarding a different parameter of the monitored fluid.

8. The method of claim 7 wherein the informa¬ tion regarding the different parameters is information derived from in-line real-time tests of values of the different parameters existing simultaneously.

9. The method of claim 1 wherein the component parameter is the concentration of a specific fluid component.

10. The method of claim 9 wherein the component is oxygen gas dissolved in the fluid.

11. The method of claim 9 wherein the component is the hydrogen ion content of the fluid.

12. The method of claim 1 further comprising the steps of: transmitting the signal from the fluid site to a remote location, and analyzing the carried information at the remote location to determine in real time the condi¬ tion of the monitored fluid.

13. The method of claim 12 further comprising the steps of: determining at the remote location the steps necessary to control the condition of the monitored fluid, and initiating corrective action based on the determination.

14. The method of claim 13 further comprising the steps of: transmitting a control signal from the remote location to the site of the monitored fluid in accordance with the determination, and modifying the composition of the monitored fluid in response to the control signal.

15. The method of claim 14 wherein the trans¬ mission step is performed over a telephone communica¬ tion link between the remote location and the system.

16. The method of claim 14 further comprising the step of initiating the transmission in response to an interrogation signal from the remote location.

17. The method of claim 14 further comprising the step of initiating the transmission in accordance with a predetermined schedule.

18. The method of claim 14 further comprising the step of initiating from the site of central system the transmission in response to information derived in the monitoring step.

19. The method of claim 14 further comprising the steps of: storing data derived in the monitoring step and subsequently generating the signal from the stored data representative of the history of the monitored parameter of the fluid.

20. The method of claim 14 wherein the trans¬ mission step is initiated at programmed intervals to transmit the plurality of signals for analysis to the remote location, and is initiated at more frequent intervals to test the information for specific charac¬ teristics.

21. A metalworking fluid monitoring central system serving one or more of metalworking machines, comprising: a central reservoir containing a volume of aqueous metalworking fluid sufficient to service the of machines; means for recirculating the fluid through the machines and the reservoir; a fluid monitor connected in-line with the central system, the monitor including a plurality of sensors, each sensor being capable of monitoring a different component parameter of fluid circulated through the monitor; means for circulating the fluid through the monitor and through at least a portion of the central system; and means for generating signals in real-time containing the information relating to each of the monitored component parameters of the monitored fluid.

22. The system of claim 21 further comprising means for modifying the composition of the monitored fluid in response to the information carried by the generated signals.

23. The system of claim 22 wherein the fluid composition modifying means comprises a fluid compo¬ nent source connected to the central system and a fluid flow control device operable in response to the information carried by the signals to control the introduction of the component from the source into the fluid.

24. The system of claim 21 further comprising: means for comparing the generated signals with stored fluid condition criteria and for program¬ ming a predetermined response to an anticipated result of the comparison; and means for generating a response signal carrying information for controlling the composition of the fluid in accordance with the predetermined response.

25. The system of claim 21 wherein one of the sensors is a sensor for measuring the pH of the fluid.

26. The system of claim 21 wherein one of the sensors is a sensor for measuring the concentration of oxygen dissolved in the fluid.

27. The system of claim 21 wherein one of the sensors is a sensor for measuring the temperature of the fluid and the system further comprises means for modifying the information from the signal from another one of the sensors in accordance with the measured temperature.

28. The system of claim 21 wherein the sensors include a sensor for measuring the electrical conduc¬ tivity of the fluid.

29. A metalworking fluid monitoring system for processing in real-time information for determining the composition of an aqueous metalworking fluid recirculated in a liquid coolant central system serving different pluralities of metalworking machines, each of the pluralities of machines being located at a different one of a plurality of metalworking plants, comprising: a central monitoring facility having means for analyzing data received from the plants and for generating signals containing information to control the compositions of metalworking fluids as a result of the analyses; means for selectively establishing a uommu- nications link between the monitoring facility and a selected one of the plants; a central reservoir at each of the plants containing a volume of aqueous metalworking fluid sufficient to service the plurality of machines at the respective plant; means at each of the plants for recircu¬ lating the fluid through the machines and the reser¬ voir at the respective plant; a fluid monitor at each of the plants connected in-line with the central system at the respective plant, each monitor including means for monitoring a component parameter of the fluid cir¬ culating through the monitor; means at each of the plants for circulating the fluid through the monitor and at least a portion of the central system; means at each plant for collecting in real-time data regarding the monitored component parameter of the fluid to be controlled; and means for transmitting the data from a plant to the central monitoring facility when a communica¬ tions link is established therebetween.

30. The system of claim 29 further comprising: means for transmitting the signals con¬ taining control information from the central facility to a selected plant; and means for controlling the composition of the fluid in accordance with the signal.